1. Field of the Invention
The present invention relates in general to medical devices and, in particular, to a biopsy needle for harvesting bone marrow samples from a living bone.
2. Background Art
Bone marrow biopsy needles have been known in the art for many years. In particular, many of these needles consist of a hollow outer cylinder with a hollow inner cylinder slidable therewithin. The outer cylinder conventionally consists of a proximal end with some form of a handle and a distal end with a tapered diameter. The distal end is typically sharp, so as to allow the needle to bore through both soft and hard tissue. The hollow inner cylinder, on the other hand, typically has a distal end consisting of some form of a cutting member. The cutting member serves to sever a tissue sample from a soft tissue mass and secure the sample inside the hollow inner cylinder, before withdrawing the sample from the patient.
For instance, Burgio, U.S. Pat. No. 5,333,619, discloses a method for rigid tissue biopsy using a partial cannula within a standard hollow outer needle having a tapered end. The partial cannula is introduced into the needle when the needle has already been inserted into the tissue. To obtain the biopsy sample, the needle is rotated repeatedly in the same direction about its major axis, thus breaking off the biopsy sample into the hollow tapered portion of the needle.
In contrast, Rubinstein, U.S. Pat. No. 5,462,062, discloses a bone marrow biopsy needle with hinged blades that cut and retain a biopsy sample. The biopsy needle consists of an outer cannula with an inwardly tapered distal end, and an inner cannula having a pair of opposing blades hingedly connected to its distal end. Specifically, upon prolapsing of tissue into the outer cannula, the inner cannula is advanced forcing its hinged ends into contact with the tapered end of the outer cannula. At this point, the hinged ends are directed radially inward, thereby cutting off the biopsy core and retaining it inside the needle.
Like Rubinstein '062, U.S. Pat. No. 4,785,826 by Ward discloses a biopsy needle with a tapered outer cannula and an inner cannula positionable therein. However, instead of hinged blades, the distal end of the inner cannula in Ward '826 comprises a series of flexible, sharp, tissue capturing segments arranged in a starburst pattern. Those segments deform and close upon engagement with the tapered end of the outer cannula, thus severing the tissue housed within the device. Moreover, while the inner cannula in Rubinstein '062 is freely slidable, Ward '826 teaches the coupling of the outer cannula to the inner cannula by the mating of male and female threaded members.
Finally, Rubinstein, U.S. Pat. No. 5,595,186, discloses a bone marrow biopsy needle that utilizes a forceps-type member to obtain a sample beyond the distal end of the outer cannula. In particular, the outer cannula narrows at its distal end, thus urging pincers, positioned at the distal end of an inner tube, together until they close upon themselves beyond the opening of the distal end of the outer cannula. Upon closing, the pincers sever a tissue sample for removal from the bone.
Although these bone biopsy devices have worked well, they have experienced certain limitations. For example, many of these devices require needle movement while inside a patient's bone to sever the soft tissue sample. This movement may take the form of rotation of the inner cannula relative to the outer cannula, or vice versa, or a certain amount of horizontal or vertical movement of the needle itself inside the bone. Inasmuch as any additional movement of the needle results in potential patient discomfort and a larger wound or needle bore hole, it is a goal in the art to minimize any needle movement.
Moreover, other biopsy needles making use of inner canulas having pincers or other flexible tissue grasping portions have experienced other difficulties. In particular, the flexibility required in the tissue grasping portion of the inner cannula to clamp and sever a tissue sample from the tissue mass upon contact with the tapered end of the outer cannula leads to problems with inner cannula durability. Specifically, the tissue grasping portion of the inner canula must possess the flexibility to conform to the outer cannula taper, the strength to sever the tissue sample, and the durability and memory to readily return to its original form for repeated use. Current devices employ tissue grasping regions that are flexible enough to deform, but lack the structural integrity to return readily and easily to their original shape for repeated use. Thus, it is a goal in the art to create a tissue grasping mechanism that has both the flexibility and durability required for effective and repetitive tissue sampling on the same patient, during the same procedure. All elements of such a device are disposable after the procedure.